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Transboundary Waters Assessment Programme (TWAP)

Why must we assess transboundary water systems?

TB Water Systems of the WorldThe water systems of the world — aquifers, lakes, rivers, large marine ecosystems, and open ocean — sustain the biosphere and underpin the health and socioeconomic wellbeing of the world’s population. Many of these systems are shared by two or more nations.

The wellbeing and socioeconomic development of a significant part of the world’s population depends on these transboundary water systems, and the essential ecosystem goods and service they provide -- including freshwater for domestic, industrial and agricultural use; fisheries, tourism, transportation, water assimilation and climate regulation. Undeniable trends, however, indicate that a growing human population and its activities as well as a changing climate are modifying these systems at an increasing rate.

Map: Transboundary Water Systems of the World. Data sources: IGRAC 2012 for aquifers, TWAP Lakes Group, Naturalearthdata for rivers, NOAA 2007 for LMEs

What is the GEF TWAP?

Recognizing the value of transboundary water systems and the fact that many of them continue to be degraded and managed in fragmented ways, the indicator-based Global Environment Facility Transboundary Waters Assessment Programme (GEF TWAP) was developed. The Programme aims to provide a baseline assessment to identify and evaluate changes in these water systems caused by human activities and natural processes, and the consequences such have on dependent human populations.

At a first step, the methodologies for conducting a global assessment of the five types of transboundary water systems were developed during the TWAP Medium-sized Project (2009-2010). The TWAP Full-sized Project is currently implementing the first truly global comparative assessment for transboundary water system categories (groundwater, lakes/reservoirs, rivers, large marine ecosystems); and a thematic evaluation of the open ocean, through institutional partnerships that hope to seed future global assessment as well. The project results assist the GEF and other international organizations in setting priorities for supporting the conservation of transboundary water systems.

How are the assessment conducted?

The TWAP consists of five independent indicator-based assessment and the linkages between them, including their socioeconomic and governance-related features. The five water-category specific assessments cover 199 transboundary aquifers, 42 non-transboundary aquifers in small island developing states, 204 transboundary lakes and reservoirs, 286 transboundary river basins, 66 large marine ecosystems (and the Western Pacific Warm Pool), and the open ocean; a total of 756 international water systems. The assessed waters cover over 70% of the planet’s oceans and landmass, and about 16% of the planet’s landmass that is also underlain by transboundary aquifers. As a first global comparative assessment of transboundary waters (those shared by two or more countries), TWAP provides quantified assessment results that can inform the setting of priorities for intervention by GEF and others as well as the development of strategies on how nations and regions can meet their Sustainable Development Goals (SDGs) and targets by 2030.

The TWAP delivers the first baseline assessment of all the planet’s transboundary water resources, providing benchmarks of the current state of water systems to inform policy, encourage knowledge exchange, identify and classify water bodies at risk and increase awareness of the importance to protect transboundary waters at relatively low risk and mitigate the states of systems at moderate to highest risk. The TWAP assessment is the first global assessment that uses quantified indicators of system states, pressures and impacts under three broad themes: biophysical, socioeconomic, and governance. Results are summarized into five relative levels of system risk - lowest, low, moderate, high, and highest - which are amenable to system and regional scale comparisons. As such, TWAP is poised to help identify core indicators to support national monitoring and reporting of targets required to realize the Sustainable Development Goals for the period 2015 – 2030. TWAP freshwater indicators map to SDG 6 on Clean Water and Sanitation, notably Target 6.6 (protection and restoration of mountains, forests, wetlands, rivers, aquifers and lakes). TWAP marine indicators support SDG 14 on Oceans, Seas and Marine Resources, and all its targets.

The United Nations Environment Programme (UNEP) is the implementing agency and the strategic partnerships formalized through the TWAP are shown in section Partners. Each partner engages a broad network of experts that evaluate transboundary water systems thematically or geographically, and comparatively, within each water system category. They employ a range of tools in such efforts, including mathematical models and geographical information systems to examine basin states.

TWAP Results

The assessment results are organized into five technical reports and a sixth volume that provides a cross-category analysis of status and trends. A Summary for Policy Makers (SPM) accompanies each volume.


In addition, the data and indicators generated though this transboundary assessment are organized and presented in a common data portal linking the five individual water system databases that contain more detailed data and information.

TWAP Indicator-Based Assessment Data Processing & Product Delivery System

Data processing & Product Delivery

Web-based access of data and indicators used and analysed by the GEF TWAP. Conceptual diagram by L. McManus with images by Jason C. Fisher, Tracey Saxby and Jane Thomas, Integration and Application Network, University of Maryland Center for Environmental Science ( and Database Clip Art from VECTOR.ME


GEF TWAP Project Coordination Unit (PCU)

United Nations Environment Programme (UNEP) | P.O. Box 30552 (00100) | Nairobi, Kenya | E-mail:

Liana Talaue McManus, Project Manager | E-mail:

Joana Akrofi, Programme Officer | E-mail:

Kaisa Uusimaa, Associate Programme Officer |






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